Human acute myeloid leukemia (AML) is an aggressive blood cancer with a high mortality rate and poor survival outcomes. The majority of AML patients die from complications arising from bone marrow failure which causes decreased production of blood forming cells. However, we lack fundamental knowledge regarding the mechanism driving this phenomenon. Building upon recent data which shows near complete depletion of hematopoietic stem and progenitors during AML expansion in human AML xenografts which occurred even with low level of disease burden, the proposed work will define whether AML cell expansion displaces normal stem and progenitors from the bone marrow environment into peripheral circulation (Aim 1) whereby they become entrapped in the splenic endothelial and perivascular niche. This project also aims to characterize the splenic endothelial and perivascular niche which remains poorly defined with respect to its cellular taxonomy and ability to provide critical niche factors (Aim 2). These studies will be complemented by investigating the unique oxysterol, 27-hydroxycholesterol, produced by AML cells in the dysregulation of normal hematopoiesis in a paracrine manner (Aim 3). This work will be performed under the primary mentorship of Dr. Ravi Majeti, an expert in the genetic characterization and therapeutic targeting of AML cells using primary human AML xenografts. My co- mentors, Dr. Irving Weissman and Dr. Hiro Nakauchi, are both renowned for their knowledge and expertise in the characterization of hematopoietic stem and progenitors cells in the bone marrow and spleen. This work will be conducted at Stanford University School of Medicine, a world-class research institution. The results of the proposed work have the potential to translate existing, non-toxic and FDA approved drugs into early phase clinical trials in a disease population that is very difficult to treat. If funded, this award will allow me to pursue a rigorous training plan in normal and malignant hematopoiesis, enabling me to expand my research across disciplines, learn new techniques, and acquire the knowledge and skills to establish an independent laboratory focused on the reversal of bone marrow failure in AML.